Durness

This 83-m cave is a geological oddity, a hybrid. Enter on the shore via the outer chamber, a sea cave created by wave action along a fault in the rock; it once stretched the 600 m length of the sea gorge and you can still make out fragments of the collapsed roof and walls. From here you follow a walkway over the flooded middle chamber, which has a waterfall when in spate. You can come this far free, any day any time, as the sea only reaches the cave on the highest tides. To go further you have to join the tour, which takes a little boat across the pool to access the inner chamber. This is karstic, created by stream water flowing through limestone, and the two caves have combined. No access after rainfall.

The most north-westerly point on the Scottish mainland. Not the most northerly, that's Dunnet Head near Thurso, but certainly the most remote. There's no through road, so you take a little ferry from Keoldale (1½ miles south of Durness) across the Kyle of Durness. (The boat can fit one or two bikes, but check ahead.) A minibus meets the ferry and lurches slowly along 11 miles of rough track, taking an hour to the Cape. There's the small "Ozone Cafe", a Stevenson lighthouse (still in use; you can't go in) and windswept cliffs with whirling seabirds. The minibus goes back after 50 min. The whole Cape is an SSSI. It's also a military live-fire training range, and public access is closed when the range is in use, normally in spring and autumn M-Sa. To get in by land, leave the main road at Sarsgrum at the head of the Kyles, and walk along the west shore till you pick up the track. It's 18 miles each way, less when the tide is out and you can wade across the river.

Only just worth the money, but it's over a beautiful beach. No pre-booking as it's so weather-dependent. If only the Vikings had discovered this mode of transport.